Discussion:
Heater connection
(too old to reply)
Alex
2008-04-12 11:27:30 UTC
Permalink
Hello.
For the 12.6/6.3V heater tubes, with a centre-tapped heater, such as 12AX7,
etc., apparently one can ground pin 9 and supply 6.3V to pins 4 and 5, or
alternatively, ground pins 4 and 5 and supply 6.3V to pin 9.

I am wondering, is there a preferred way of doing it? Which connection
results in a lower hum?

If there is no difference hum-wise, perhaps grounding of pin 9 is more
convenient in case one wants to plug in a 6.3V only tube, e.g. ECC85 or
Russian 6N2P -- less rewiring will be needed.

What do you think?

Regardss,
Alex
Phil Allison
2008-04-12 12:02:11 UTC
Permalink
"Alex"
Post by Alex
For the 12.6/6.3V heater tubes, with a centre-tapped heater, such as 12AX7,
etc., apparently one can ground pin 9 and supply 6.3V to pins 4 and 5, or
alternatively, ground pins 4 and 5 and supply 6.3V to pin 9.
I am wondering, is there a preferred way of doing it? Which connection
results in a lower hum?
** Neither.

The correct ways with AC heaters are:

1. Use a centre tapped 6.3 volt heater supply or

2 Use a pair or 100 ohm resistors to provide a simulated centre tap or

3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with wiper
grounded & adjusted for least hum.


If you want to avoid all such tedious hum issues - use 6.3 volt regulated
DC.



...... Phil
Ian Thompson-Bell
2008-04-12 16:17:37 UTC
Permalink
Post by Phil Allison
"Alex"
Post by Alex
For the 12.6/6.3V heater tubes, with a centre-tapped heater, such as 12AX7,
etc., apparently one can ground pin 9 and supply 6.3V to pins 4 and 5, or
alternatively, ground pins 4 and 5 and supply 6.3V to pin 9.
I am wondering, is there a preferred way of doing it? Which connection
results in a lower hum?
** Neither.
1. Use a centre tapped 6.3 volt heater supply or
2 Use a pair or 100 ohm resistors to provide a simulated centre tap or
3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with wiper
grounded & adjusted for least hum.
If you want to avoid all such tedious hum issues - use 6.3 volt regulated
DC.
And even easier, with the tube the OP mentioned, use a 12V regulated dc
supply.

Cheers

Ian
Phil Allison
2008-04-13 01:48:50 UTC
Permalink
"Ian Thompson-Bell"
Post by Ian Thompson-Bell
Post by Phil Allison
"Alex"
Post by Alex
For the 12.6/6.3V heater tubes, with a centre-tapped heater, such as 12AX7,
etc., apparently one can ground pin 9 and supply 6.3V to pins 4 and 5, or
alternatively, ground pins 4 and 5 and supply 6.3V to pin 9.
I am wondering, is there a preferred way of doing it? Which connection
results in a lower hum?
** Neither.
1. Use a centre tapped 6.3 volt heater supply or
2 Use a pair or 100 ohm resistors to provide a simulated centre tap or
3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with
wiper grounded & adjusted for least hum.
If you want to avoid all such tedious hum issues - use 6.3 volt
regulated DC.
And even easier, with the tube the OP mentioned, use a 12V regulated dc
supply.
** The Ian T-B autistic mental defective has selective eyesight - it only
sees what it wants to see.

So it is totally wrong - again ....




..... Phil
Patrick Turner
2008-04-13 03:57:37 UTC
Permalink
Post by Ian Thompson-Bell
Post by Phil Allison
"Alex"
Post by Alex
For the 12.6/6.3V heater tubes, with a centre-tapped heater, such as 12AX7,
etc., apparently one can ground pin 9 and supply 6.3V to pins 4 and 5, or
alternatively, ground pins 4 and 5 and supply 6.3V to pin 9.
I am wondering, is there a preferred way of doing it? Which connection
results in a lower hum?
** Neither.
1. Use a centre tapped 6.3 volt heater supply or
2 Use a pair or 100 ohm resistors to provide a simulated centre tap or
3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with wiper
grounded & adjusted for least hum.
If you want to avoid all such tedious hum issues - use 6.3 volt regulated
DC.
And even easier, with the tube the OP mentioned, use a 12V regulated dc
supply.
Cheers
Ian 12V isn't the right voltage for heaters where 2 x 6.3V heaters are connected in series.
It should be 12.6V

This is easily gained by using 3 leg 12V regulator chip but with a
series diode in the adjust
with cathode to -V rail.

Patrick Turner.
Ian Thompson-Bell
2008-04-13 10:57:27 UTC
Permalink
Post by Patrick Turner
Post by Ian Thompson-Bell
Post by Phil Allison
"Alex"
Post by Alex
For the 12.6/6.3V heater tubes, with a centre-tapped heater, such as 12AX7,
etc., apparently one can ground pin 9 and supply 6.3V to pins 4 and 5, or
alternatively, ground pins 4 and 5 and supply 6.3V to pin 9.
I am wondering, is there a preferred way of doing it? Which connection
results in a lower hum?
** Neither.
1. Use a centre tapped 6.3 volt heater supply or
2 Use a pair or 100 ohm resistors to provide a simulated centre tap or
3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with wiper
grounded & adjusted for least hum.
If you want to avoid all such tedious hum issues - use 6.3 volt regulated
DC.
And even easier, with the tube the OP mentioned, use a 12V regulated dc
supply.
Cheers
Ian 12V isn't the right voltage for heaters where 2 x 6.3V heaters are connected in series.
It should be 12.6V
This is easily gained by using 3 leg 12V regulator chip but with a
series diode in the adjust
with cathode to -V rail.
Patrick Turner.
Strictly speaking, yes it should be 12.6V, but that is only a nominal
value and tubes were designed to expect at least a +- 5% variation in
mains supply and hence heater supply. Emission is hardly affected at all
when running from 12V dc and heater life is likely to be extended.

Cheers

Ian
Patrick Turner
2008-04-13 13:59:11 UTC
Permalink
Post by Ian Thompson-Bell
Post by Patrick Turner
Post by Ian Thompson-Bell
Post by Phil Allison
"Alex"
Post by Alex
For the 12.6/6.3V heater tubes, with a centre-tapped heater, such as 12AX7,
etc., apparently one can ground pin 9 and supply 6.3V to pins 4 and 5, or
alternatively, ground pins 4 and 5 and supply 6.3V to pin 9.
I am wondering, is there a preferred way of doing it? Which connection
results in a lower hum?
** Neither.
1. Use a centre tapped 6.3 volt heater supply or
2 Use a pair or 100 ohm resistors to provide a simulated centre tap or
3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with wiper
grounded & adjusted for least hum.
If you want to avoid all such tedious hum issues - use 6.3 volt regulated
DC.
And even easier, with the tube the OP mentioned, use a 12V regulated dc
supply.
Cheers
Ian 12V isn't the right voltage for heaters where 2 x 6.3V heaters are connected in series.
It should be 12.6V
This is easily gained by using 3 leg 12V regulator chip but with a
series diode in the adjust
with cathode to -V rail.
Patrick Turner.
Strictly speaking, yes it should be 12.6V, but that is only a nominal
value and tubes were designed to expect at least a +- 5% variation in
mains supply and hence heater supply. Emission is hardly affected at all
when running from 12V dc and heater life is likely to be extended.
Cheers
Ian
You are quite right of course, 12.0V is near enough for signal tubes at
least.
I still use the diode though and tube life is only threatened
when IH is extremely low, or over 10% too high.
I think RDH4 say +/- 10% VH is OK, so from 5.7V to 7V.

The Jolida 502 I am working on to improve had 7.15Vrms everywehere.
We get 252Vrms mains, supposed to be 240Vrms, and if that was so,
VH would be 6.8Vac, still wrong, but it would be right if mains =
220Vrms
where VH would then be 6.24V.

This indicates the Chinese mains tranny was originally designed for
220Vrms, and no
allowance has been made for Oz voltages at 252Vrms.
And and one reason why it is mechanically noisy.

Patrick Turner.
Ian Thompson-Bell
2008-04-14 08:32:02 UTC
Permalink
Post by Patrick Turner
Post by Ian Thompson-Bell
Post by Patrick Turner
Post by Ian Thompson-Bell
Post by Phil Allison
"Alex"
Post by Alex
For the 12.6/6.3V heater tubes, with a centre-tapped heater, such as 12AX7,
etc., apparently one can ground pin 9 and supply 6.3V to pins 4 and 5, or
alternatively, ground pins 4 and 5 and supply 6.3V to pin 9.
I am wondering, is there a preferred way of doing it? Which connection
results in a lower hum?
** Neither.
1. Use a centre tapped 6.3 volt heater supply or
2 Use a pair or 100 ohm resistors to provide a simulated centre tap or
3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with wiper
grounded & adjusted for least hum.
If you want to avoid all such tedious hum issues - use 6.3 volt regulated
DC.
And even easier, with the tube the OP mentioned, use a 12V regulated dc
supply.
Cheers
Ian 12V isn't the right voltage for heaters where 2 x 6.3V heaters are connected in series.
It should be 12.6V
This is easily gained by using 3 leg 12V regulator chip but with a
series diode in the adjust
with cathode to -V rail.
Patrick Turner.
Strictly speaking, yes it should be 12.6V, but that is only a nominal
value and tubes were designed to expect at least a +- 5% variation in
mains supply and hence heater supply. Emission is hardly affected at all
when running from 12V dc and heater life is likely to be extended.
Cheers
Ian
You are quite right of course, 12.0V is near enough for signal tubes at
least.
I still use the diode though and tube life is only threatened
when IH is extremely low, or over 10% too high.
I think RDH4 say +/- 10% VH is OK, so from 5.7V to 7V.
The Jolida 502 I am working on to improve had 7.15Vrms everywehere.
We get 252Vrms mains, supposed to be 240Vrms, and if that was so,
VH would be 6.8Vac, still wrong, but it would be right if mains =
220Vrms
where VH would then be 6.24V.
This indicates the Chinese mains tranny was originally designed for
220Vrms, and no
allowance has been made for Oz voltages at 252Vrms.
And and one reason why it is mechanically noisy.
Patrick Turner.
Th other facter is of course the load regulation of the heater winding
which depends on the transformer construction and how close the heater
current comes to the rated load .

Whatever happened to mains trannys with tapped primaries?

Cheers

Ian
Nick Gorham
2008-04-14 10:10:57 UTC
Permalink
Post by Ian Thompson-Bell
Whatever happened to mains trannys with tapped primaries?
Cheers
Ian
They are there if you want to pay for them, Sowter have two standard
primary layouts

European type: 240, 220, 200, 0, -10 volts taps.

World-wide type: Two separate windings with 120, 110, 0 volts taps.
--
Nick
Ian Thompson-Bell
2008-04-14 10:36:33 UTC
Permalink
Post by Nick Gorham
Post by Ian Thompson-Bell
Whatever happened to mains trannys with tapped primaries?
Cheers
Ian
They are there if you want to pay for them, Sowter have two standard
primary layouts
European type: 240, 220, 200, 0, -10 volts taps.
World-wide type: Two separate windings with 120, 110, 0 volts taps.
Ah, good old Brian.

Cheers

Ian
Robert Casey
2008-04-15 04:54:58 UTC
Permalink
Post by Nick Gorham
European type: 240, 220, 200, 0, -10 volts taps.
World-wide type: Two separate windings with 120, 110, 0 volts taps.
Some cheaper transformers just did 110, 120, 220 and 240 as a single
winding. Which meant that half the winding didn't do any work if ran
off of 120V. I have a couple of radios from Europe that have this
set-up, and as I have avaliable ***@15A outlets (a pair of 120V lines
180 degrees out of phase) I set the radio to 240V to make life easier on
teh primary winding (half the current than if I set it to 120V).
Phil Allison
2008-04-15 08:42:41 UTC
Permalink
"Robert Casey"
Post by Robert Casey
Some cheaper transformers just did 110, 120, 220 and 240 as a single
winding. Which meant that half the winding didn't do any work if ran off
of 120V.
** The AC transformers used in Marshall and Fender valve guitar amps were
all like that - right through the 70s and most of the 80s.

These were 250 to 350 VA jobs too.



..... Phil
Patrick Turner
2008-04-14 10:54:28 UTC
Permalink
Post by Ian Thompson-Bell
Post by Patrick Turner
Post by Ian Thompson-Bell
Post by Patrick Turner
Post by Ian Thompson-Bell
Post by Phil Allison
"Alex"
Post by Alex
For the 12.6/6.3V heater tubes, with a centre-tapped heater, such as 12AX7,
etc., apparently one can ground pin 9 and supply 6.3V to pins 4 and 5, or
alternatively, ground pins 4 and 5 and supply 6.3V to pin 9.
I am wondering, is there a preferred way of doing it? Which connection
results in a lower hum?
** Neither.
1. Use a centre tapped 6.3 volt heater supply or
2 Use a pair or 100 ohm resistors to provide a simulated centre tap or
3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with wiper
grounded & adjusted for least hum.
If you want to avoid all such tedious hum issues - use 6.3 volt regulated
DC.
And even easier, with the tube the OP mentioned, use a 12V regulated dc
supply.
Cheers
Ian 12V isn't the right voltage for heaters where 2 x 6.3V heaters are connected in series.
It should be 12.6V
This is easily gained by using 3 leg 12V regulator chip but with a
series diode in the adjust
with cathode to -V rail.
Patrick Turner.
Strictly speaking, yes it should be 12.6V, but that is only a nominal
value and tubes were designed to expect at least a +- 5% variation in
mains supply and hence heater supply. Emission is hardly affected at all
when running from 12V dc and heater life is likely to be extended.
Cheers
Ian
You are quite right of course, 12.0V is near enough for signal tubes at
least.
I still use the diode though and tube life is only threatened
when IH is extremely low, or over 10% too high.
I think RDH4 say +/- 10% VH is OK, so from 5.7V to 7V.
The Jolida 502 I am working on to improve had 7.15Vrms everywehere.
We get 252Vrms mains, supposed to be 240Vrms, and if that was so,
VH would be 6.8Vac, still wrong, but it would be right if mains =
220Vrms
where VH would then be 6.24V.
This indicates the Chinese mains tranny was originally designed for
220Vrms, and no
allowance has been made for Oz voltages at 252Vrms.
And and one reason why it is mechanically noisy.
Patrick Turner.
Th other facter is of course the load regulation of the heater winding
which depends on the transformer construction and how close the heater
current comes to the rated load .
Whatever happened to mains trannys with tapped primaries?
Bean counters ate them up then vomited them down the toilet.

Having many taps on mains trannies can be a curse.
One sets the tap to suit the mains in your area, then forget all about
it and
after biasing the fixed bias, you move house, or sell the amp
and the next time the amp is used the HT is way too high and heaters,
and OP tubes glow red.

Then someone has to wake up what's happening.

Unwanted drama.

Better is to have a less critical set up of the amp.

Its not always possible.

In the Jolida I have here to fix, there
are two primaries for either 220V in series or presumably 110V in
parallel.
This will suit Europe with 230V, and US with 110V.

But in Oz we have 252V most days where I am.

The local importers of Jolida had to change caps in the PSU
and bias the tubes for lower current to get the amp past a month of use.

It is possible to simply place a series 35 ohm resistor in series with
the
mains input, but I figured out that to get a drop of 32V at 0.9 amps
input
current means the R will put out 28 watts, so should be rated for 100W.

Possibly there would be a certain value of inductance which would work
instead of the series R, but the wire size would need to be 1.0mm dia,
and maybe 100mH, which is a fair sized inductor to make and fit in.

I put 25ohms in series with 235uF resevoir cap and bridge rectifier to
allow the B+ to be lowered to where it should be, and also to
limit C charge currents and reduce PT noise. I put some series R
to reduce input tube heater voltages.



Patrick Turner.
Post by Ian Thompson-Bell
Cheers
Ian
John Byrns
2008-04-14 13:08:17 UTC
Permalink
Post by Patrick Turner
In the Jolida I have here to fix, there
are two primaries for either 220V in series or presumably 110V in
parallel.
This will suit Europe with 230V, and US with 110V.
The US does not have 110V, the standard in the US is 120V, so two 110V
primaries in parallel would not suit the US.


Regards,

John Byrns
--
Surf my web pages at, http://fmamradios.com/
Patrick Turner
2008-04-14 14:01:32 UTC
Permalink
Post by John Byrns
Post by Patrick Turner
In the Jolida I have here to fix, there
are two primaries for either 220V in series or presumably 110V in
parallel.
This will suit Europe with 230V, and US with 110V.
The US does not have 110V, the standard in the US is 120V, so two 110V
primaries in parallel would not suit the US.
Regards,
John Byrns
I thought it was officially 117V for the US.

But we see 240:110V step down trannies for sale for US made gear.

Mains V does vary considerably though.

I provide 2 x 120V windings on my PT with each winding having
taps at 110V and 100V so there is considerable choice.

In my latest 845 amps there are a total of 48 connections
to multiple windings to suit a wide range of tubes
if 845 become unavailable.
Even the OPT can be re-configured to suit many other tubes besides the 2
x 845 in parallel.
There are a total of 12 windings and 24 connections.

Patrick Turner.
Post by John Byrns
--
Surf my web pages at, http://fmamradios.com/
John Byrns
2008-04-14 14:39:14 UTC
Permalink
Post by Patrick Turner
Post by John Byrns
Post by Patrick Turner
In the Jolida I have here to fix, there
are two primaries for either 220V in series or presumably 110V in
parallel.
This will suit Europe with 230V, and US with 110V.
The US does not have 110V, the standard in the US is 120V, so two 110V
primaries in parallel would not suit the US.
I thought it was officially 117V for the US.
As far as I know that is just an Urban Legend, the standard as I have
seen it is 120VAC with plus and minus tolerances that I forget. I'm not
sure where 117V came from, it seems to have been used by many old radio
manufacturers, and perhaps by manufacturers of other equipment, perhaps
as a sort of a design center value, but as near as I can tell it was not
an official standard, 120VAC has been the standard for a very long time.
Post by Patrick Turner
But we see 240:110V step down trannies for sale for US made gear.
Mains V does vary considerably though.
I provide 2 x 120V windings on my PT with each winding having
taps at 110V and 100V so there is considerable choice.
Line voltages here in the US seem to run from 120VAC up, I have seen
them as high as 135VAC. I suspect lower voltages are seen mostly out in
the boonies at times of day when the load is heaviest.


Regards,

John Byrns
--
Surf my web pages at, http://fmamradios.com/
Robert Casey
2008-04-15 04:46:31 UTC
Permalink
Post by John Byrns
Line voltages here in the US seem to run from 120VAC up, I have seen
them as high as 135VAC. I suspect lower voltages are seen mostly out in
the boonies at times of day when the load is heaviest.
Hot Summer days can make the line drop to 110V (air conditioning load).
Or lower. Not normal, though.
John Byrns
2008-04-13 15:45:05 UTC
Permalink
Post by Patrick Turner
Post by Ian Thompson-Bell
Post by Phil Allison
"Alex"
Post by Alex
For the 12.6/6.3V heater tubes, with a centre-tapped heater, such as 12AX7,
etc., apparently one can ground pin 9 and supply 6.3V to pins 4 and 5, or
alternatively, ground pins 4 and 5 and supply 6.3V to pin 9.
I am wondering, is there a preferred way of doing it? Which connection
results in a lower hum?
** Neither.
1. Use a centre tapped 6.3 volt heater supply or
2 Use a pair or 100 ohm resistors to provide a simulated centre tap or
3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with wiper
grounded & adjusted for least hum.
If you want to avoid all such tedious hum issues - use 6.3 volt regulated
DC.
And even easier, with the tube the OP mentioned, use a 12V regulated dc
supply.
Cheers
Ian 12V isn't the right voltage for heaters where 2 x 6.3V heaters are
connected in series.
It should be 12.6V
This is easily gained by using 3 leg 12V regulator chip but with a
series diode in the adjust
with cathode to -V rail.
But then there are the people that like to run 12AX7s with 10V on the
heater.


Regards,

John Byrns
--
Surf my web pages at, http://fmamradios.com/
Patrick Turner
2008-04-13 16:25:52 UTC
Permalink
Post by John Byrns
Post by Patrick Turner
Post by Ian Thompson-Bell
Post by Phil Allison
"Alex"
Post by Alex
For the 12.6/6.3V heater tubes, with a centre-tapped heater, such as 12AX7,
etc., apparently one can ground pin 9 and supply 6.3V to pins 4 and 5, or
alternatively, ground pins 4 and 5 and supply 6.3V to pin 9.
I am wondering, is there a preferred way of doing it? Which connection
results in a lower hum?
** Neither.
1. Use a centre tapped 6.3 volt heater supply or
2 Use a pair or 100 ohm resistors to provide a simulated centre tap or
3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with wiper
grounded & adjusted for least hum.
If you want to avoid all such tedious hum issues - use 6.3 volt regulated
DC.
And even easier, with the tube the OP mentioned, use a 12V regulated dc
supply.
Cheers
Ian 12V isn't the right voltage for heaters where 2 x 6.3V heaters are
connected in series.
It should be 12.6V
This is easily gained by using 3 leg 12V regulator chip but with a
series diode in the adjust
with cathode to -V rail.
But then there are the people that like to run 12AX7s with 10V on the
heater.
Regards,
John Byrns
Well yes, and they claim the sound becomes especially good
where with 12.6V it was not as special.

But perhaps temperature of the cathode is lower, hence noise is lower.
But then emission is lower so gm would be lower, increasing noise.

Tubes work with 10v instead of 12.6V. That's about all I know.

Patrick Turner.
usomen
Post by John Byrns
--
Surf my web pages at, http://fmamradios.com/
Iain Churches
2008-04-13 17:03:06 UTC
Permalink
Post by Patrick Turner
Post by John Byrns
But then there are the people that like to run 12AX7s with 10V on the
heater.
Well yes, and they claim the sound becomes especially good
where with 12.6V it was not as special.
But perhaps temperature of the cathode is lower, hence noise is lower.
But then emission is lower so gm would be lower, increasing noise.
Tubes work with 10v instead of 12.6V. That's about all I know.
It is difficult to know if there really is anything in this.
People talk about running 6V3 heaters at 5V also.
They claim superior sound, but do not seem to be
able to qualify what they mean.

Does anyone have any experience of this? Any benefits
(other than perhaps longer heater life?)

Iain
John Byrns
2008-04-13 17:19:24 UTC
Permalink
Post by Iain Churches
Post by Patrick Turner
Post by John Byrns
But then there are the people that like to run 12AX7s with 10V on the
heater.
Well yes, and they claim the sound becomes especially good
where with 12.6V it was not as special.
But perhaps temperature of the cathode is lower, hence noise is lower.
But then emission is lower so gm would be lower, increasing noise.
Tubes work with 10v instead of 12.6V. That's about all I know.
It is difficult to know if there really is anything in this.
People talk about running 6V3 heaters at 5V also.
They claim superior sound, but do not seem to be
able to qualify what they mean.
Does anyone have any experience of this? Any benefits
(other than perhaps longer heater life?)
I don't have any experience beyond owning a preamp the runs its 12AX7s
with 5 volts on the heaters. I was told that this was done to reduce
the noise generated in the tube, but I don't actually know that this is
a fact.

Also many radios have a resistor in series with the heater of the
detector tube to reduce the heater voltage to 5 volts, I forget why this
is done, as best I remember it may be to reduce the "contact potential"
of the grid.


Regards,

John Byrns
--
Surf my web pages at, http://fmamradios.com/
Alex
2008-04-13 22:55:10 UTC
Permalink
Post by John Byrns
I don't have any experience beyond owning a preamp the runs its 12AX7s
with 5 volts on the heaters. I was told that this was done to reduce
the noise generated in the tube, but I don't actually know that this is
a fact.
Also many radios have a resistor in series with the heater of the
detector tube to reduce the heater voltage to 5 volts, I forget why this
is done, as best I remember it may be to reduce the "contact potential"
of the grid.
In AM detectors, a small number of "hot" electrons shoot from the cathode to
the anode and charge the anode negatively. As a result the diode becomes
somewhat reverse biased by its own thermionic emission, which adversely
affects rectification of small signals -- the"knee" from the law of 3/2
transforms into a long exponential tail. With lower cathode temperature the
anode charging negative is less pronounced. Emission current reduction is
not an issue since AM detectors typically run in uamp mode -- into 470Kohm
load. So, cathode temperature reduction helps.

I am not an expert on all the cons and pros in audio preamps, but for one
thing -- heater-to-cathode leakage will significantly reduce, especially in
Russian tubes with "dirty" heater insulation.

Regards,
Alex
Post by John Byrns
Regards,
John Byrns
--
Surf my web pages at, http://fmamradios.com/
Iain Churches
2008-04-13 18:52:35 UTC
Permalink
Post by John Byrns
Post by Iain Churches
Post by Patrick Turner
Post by John Byrns
But then there are the people that like to run 12AX7s with 10V on the
heater.
Well yes, and they claim the sound becomes especially good
where with 12.6V it was not as special.
But perhaps temperature of the cathode is lower, hence noise is lower.
But then emission is lower so gm would be lower, increasing noise.
Tubes work with 10v instead of 12.6V. That's about all I know.
It is difficult to know if there really is anything in this.
People talk about running 6V3 heaters at 5V also.
They claim superior sound, but do not seem to be
able to qualify what they mean.
Does anyone have any experience of this? Any benefits
(other than perhaps longer heater life?)
I don't have any experience beyond owning a preamp the runs its 12AX7s
with 5 volts on the heaters. I was told that this was done to reduce
the noise generated in the tube, but I don't actually know that this is
a fact.
Well, lower cathode temperature means lower noise, but....
emisssion is also lower.
Post by John Byrns
Also many radios have a resistor in series with the heater of the
detector tube to reduce the heater voltage to 5 volts, I forget why this
is done, as best I remember it may be to reduce the "contact potential"
of the grid.
Many people seem very keen indeed to fit SS regulators to tube heater
supplies. The heater voltage is probably not too critical, as 5% has
always been stated as the tolerance. However, I am very interested
in the idea of current regulation for tubes to increase the heater
longevity.


regards
Iain
keithr
2008-04-15 11:54:37 UTC
Permalink
Post by Iain Churches
Post by Patrick Turner
Post by John Byrns
But then there are the people that like to run 12AX7s with 10V on the
heater.
Well yes, and they claim the sound becomes especially good
where with 12.6V it was not as special.
But perhaps temperature of the cathode is lower, hence noise is lower.
But then emission is lower so gm would be lower, increasing noise.
Tubes work with 10v instead of 12.6V. That's about all I know.
It is difficult to know if there really is anything in this.
People talk about running 6V3 heaters at 5V also.
They claim superior sound, but do not seem to be
able to qualify what they mean.
Does anyone have any experience of this? Any benefits
(other than perhaps longer heater life?)
Iain
Just more voodoo, they probably have volume controls that go to 11.

The tubes will last longer though as long as the anode current isn't too
high, emission will be down a fraction

Keith
Iain Churches
2008-04-15 16:34:45 UTC
Permalink
Post by keithr
Post by Iain Churches
Post by Patrick Turner
Post by John Byrns
But then there are the people that like to run 12AX7s with 10V on the
heater.
Well yes, and they claim the sound becomes especially good
where with 12.6V it was not as special.
But perhaps temperature of the cathode is lower, hence noise is lower.
But then emission is lower so gm would be lower, increasing noise.
Tubes work with 10v instead of 12.6V. That's about all I know.
It is difficult to know if there really is anything in this.
People talk about running 6V3 heaters at 5V also.
They claim superior sound, but do not seem to be
able to qualify what they mean.
Does anyone have any experience of this? Any benefits
(other than perhaps longer heater life?)
Iain
Just more voodoo, they probably have volume controls that go to 11.
That's kid's stuff! I have a volume control that goes to 59:-)
It's a 60 position TKD attenuator. On the lowest position the
wiper is to ground, so I called that position "0" which makes the highest
pos 59.
Post by keithr
The tubes will last longer though as long as the anode current isn't too
high, emission will be down a fraction
Yes indeed. But is there no magical improvement in the
sound which even the au pair can hear from the kitchen??

Regards
Iain

Alex
2008-04-13 08:34:36 UTC
Permalink
Post by Phil Allison
1. Use a centre tapped 6.3 volt heater supply or
2 Use a pair or 100 ohm resistors to provide a simulated centre tap or
3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with wiper
grounded & adjusted for least hum.
If you want to avoid all such tedious hum issues - use 6.3 volt regulated
DC.
OK. I see your point -- balanced AC or DC.

What causes more hum: leakage heater-cathode or leakage/stray capacitance
heater-grid?

Since the heaters in 12AX7 are connected in series. Balancing 12.6V heater
voltage will not be able to cancel out leakage to cathodes in both triodes
at the same time.

Besides. 12V will cause more stray noise just because of capacitive coupling
to grid(s). Indeed, 6.3V is looks better. DC is the best -- no matter 6V or
12V...

Indeed it looks like better to use 6.3V.

Also I noticed, that in the new Sovtek 12AT7 tubes the cathodes run cool at
the nominal 12.6V -- you hardly see any glow. Why is that? To reduce noise
and to extend tube life? If it is beneficial, perhaps the heater voltage can
be reduced to 5.5V or so for "standard" tubes in the small-signal stages,
where high peak emission is not required.

Regards,
Alex
Phil Allison
2008-04-13 09:43:49 UTC
Permalink
"Alex"
Post by Phil Allison
Post by Phil Allison
1. Use a centre tapped 6.3 volt heater supply or
2 Use a pair or 100 ohm resistors to provide a simulated centre tap or
3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with
wiper
Post by Phil Allison
grounded & adjusted for least hum.
If you want to avoid all such tedious hum issues - use 6.3 volt
regulated
Post by Phil Allison
DC.
OK. I see your point -- balanced AC or DC.
What causes more hum: leakage heater-cathode or leakage/stray capacitance
heater-grid?
** Depends on the impedance at the particular grid, if higher than say 50
kohms - stray C and R leakage are dominant causes.

Explains why DC heaters are the way to go with high sensitivity & high
impedance circuits.

Check out the schems of any tube condenser mic, source independences range
up to the in the *gigohms* with them.
Post by Phil Allison
Since the heaters in 12AX7 are connected in series. Balancing 12.6V heater
voltage will not be able to cancel out leakage to cathodes in both triodes
at the same time.
** Huh - it balances neither.
Post by Phil Allison
Indeed it looks like better to use 6.3V.
** With the provisos as posted previously.
Post by Phil Allison
Also I noticed, that in the new Sovtek 12AT7 tubes the cathodes run cool at
the nominal 12.6V
** Bollocks.

The cathodes get just as hot as with any other make of 'T7 - or any tube.
Post by Phil Allison
-- you hardly see any glow.
** Proves only the fact the light will not penetrate a solid matter.

Get yourself a good magnifier - pal.

Before leaping to dumb conclusions.



..... Phil
Patrick Turner
2008-04-13 13:49:37 UTC
Permalink
Post by Phil Allison
Post by Phil Allison
1. Use a centre tapped 6.3 volt heater supply or
2 Use a pair or 100 ohm resistors to provide a simulated centre tap or
3 Use a 100 ohm wire-wound pot wired across the 6.3 volt supply with
wiper
Post by Phil Allison
grounded & adjusted for least hum.
If you want to avoid all such tedious hum issues - use 6.3 volt
regulated
Post by Phil Allison
DC.
OK. I see your point -- balanced AC or DC.
The DC does not need to be balanced.

eg, 12.6Vdc can be applied to pins 4 and 5 of a 12AX7.

But to balance applied AC, only 6.3 V can be used with
opposite phased 3.15V applied to pins 4&5 and pin 9.

The current should be brought to the tube socket in two wires to these
pins,
then a ground referencing connection made to 0V from the negative pin,
so no ac or dc current flows ever flows in the 0V rail.
With dc heating, the heater becomes slightly positive,
which is supposed to be better than having the heater slightly negative.

But there is nothing to stop you referencing or biasing the whole DC or
balanced AC heater
supply at anywhere up to +70V in small signal tubes because it could be
very
useful where you have a cathode follower or µ-follower, or SRPP.
I recently biased up the revised balanced 6.3Vac heater supply in a
Jolida 502 amp at +65V,
and the hum I did have some bother with virtually vanished.
Post by Phil Allison
What causes more hum: leakage heater-cathode or leakage/stray capacitance
heater-grid?
Since the heaters in 12AX7 are connected in series. Balancing 12.6V heater
voltage will not be able to cancel out leakage to cathodes in both triodes
at the same time.
Correct, although if both 1/2 of 12AX7 are in parallel, maybe its OK,
but to play it safe, a 6.3Vac heater should be applied as 2 phases of
3.15Vac to
pins 4&5, and pin 9.
Post by Phil Allison
Besides. 12V will cause more stray noise just because of capacitive coupling
to grid(s). Indeed, 6.3V is looks better. DC is the best -- no matter 6V or
12V...
Agreed, but in a power amp, perhaps only the input tube need have the
specially done quiet heating with DC.
Post by Phil Allison
Indeed it looks like better to use 6.3V.
Also I noticed, that in the new Sovtek 12AT7 tubes the cathodes run cool at
the nominal 12.6V -- you hardly see any glow. Why is that? To reduce noise
and to extend tube life? If it is beneficial, perhaps the heater voltage can
be reduced to 5.5V or so for "standard" tubes in the small-signal stages,
where high peak emission is not required.
"Glow" is usually from the exposed ends of folded heater elements insde
the cathode tube.
If the heating element is tucked well inside the cathode tube then the
glow is less visible.

Patrick Turner.
Post by Phil Allison
Regards,
Alex
mick
2008-04-13 14:00:57 UTC
Permalink
Post by Alex
Hello.
For the 12.6/6.3V heater tubes, with a centre-tapped heater, such as
12AX7, etc., apparently one can ground pin 9 and supply 6.3V to pins 4
and 5, or alternatively, ground pins 4 and 5 and supply 6.3V to pin 9.
I am wondering, is there a preferred way of doing it? Which connection
results in a lower hum?
If there is no difference hum-wise, perhaps grounding of pin 9 is more
convenient in case one wants to plug in a 6.3V only tube, e.g. ECC85 or
Russian 6N2P -- less rewiring will be needed.
What do you think?
It looks to me as if everyone so far has misunderstood you, Alex... :-)

If you have a look through the glass, I'll think you'll find that it
doesn't matter which way you do it. Personally, I've always grounded pin
9 when using 6.3v heaters. I can't remember why I started doing it that
way - it just seemed to make more sense at the time, I suppose!
--
Mick (Working in a M$-free zone!)
Web: http://www.nascom.info http://mixpix.batcave.net
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